Data synchronisation process, and transmission and reception interfaces

ABSTRACT

Especially simple interfaces for outputting or receiving data are proposed, which can be operated by an especially simple method. It is provided that three different levels can be realized on the bus. One of these levels (V 0 ) is used to generate a synchronization signal for the successive transmission of a high bit or a low bit. The individual bits are realized by means of the other two voltage levels (V 2 , V 1 ). In a modification, via interfaces or connecting lines, items of information that are represented with the aid of two different levels are exchanged. In the process, by means of different pulse lengths, both synchronization pulses and two different information pulses are generated.

PRIOR ART

[0001] The invention is based on a method for transmitting data and on interfaces for transmitting or receiving data, as generically defined by the preambles to the independent claims, and relates in particular to a voltage controller with an interface in a motor vehicle.

[0002] From German Patent Disclosure DE 35 06 118, a method for transmitting data over a data line is already known, in which a sequence of first and second states, distinguishable from one another, are transmitted over the data line. These states then represent a high bit or a low bit.

ADVANTAGES OF THE INVENTION

[0003] The method and interfaces according to the invention as defined by the characteristics of the bodies of the independent claims have the advantage over the prior art that a third state is provided, which is utilized for transmitting a synchronization signal. The synchronization can therefore be generated in the data stations involved, and can be imparted to the other stations involved over the data line. As a result, it is possible for only one of the data stations involved internally to have the means for generating a synchronization signal, while the other stations need not have any such means.

[0004] It is especially advantageous that work can also be done with two voltage levels. This advantage is attained in that both the synchronization pulses and the other two items of information, such as a zero datum and a one datum are embodied by pulses of different signal lengths. Advantageously, the pulses that include the two items of information begin simultaneously with the respective synchronization pulse. The transmission is advantageously effected between a first data station and a second station, which communicate with one another through a transmission line. It is especially advantageous that the system can also be used when there are a plurality of receivers, and that a transmission protocol is produced.

[0005] In the dependent claims, advantageous refinements of and improvements to the method and the interface of the dependent claims are disclosed. The synchronization signal becomes especially simple if it comprises putting the data line into the third state for a predetermined minimum time. The receiving station can then be synchronized to the signal edge that indicates the end of the third state. It is then simple to write in a high bit or a low bit, by writing in, after the synchronization signal, whether the data line is in the first or the second state. It is also advantageous in this regard that the length of the synchronization signal or of the high bit or a low bit does not matter, as long as they each exceed a predetermined minimum time that is needed for reliable detection of the respective state on the data line. The various states on the data line are especially simply embodied by different voltage levels.

[0006] Using the interfaces of the invention in the method for data transmission of the invention can advantageously be done in the form of using a bit-synchronized interface in the motor vehicle. An especially advantageous application of the interface is the communication between the voltage controller and the on-board electrical system of a motor vehicle. Communication between the voltage controller and the microcomputer of the digital engine electronics as a component of the engine control unit is likewise advantageously possible.

DRAWINGS

[0007] Exemplary embodiments of the invention are described in the ensuing description and shown in the drawings.

[0008]FIG. 1 schematically shows two data stations, which are connected by a data line;

[0009]FIG. 2 shows different states on the data line;

[0010]FIG. 3 shows two interfaces according to the invention; and

[0011]FIG. 5 shows a simple logic for evaluating data.

[0012]FIG. 5 also shows a realization of an interface in terms of circuitry between the voltage controller and the on-board electrical system of a motor vehicle, or the interface between the digital engine electronics (DME) and voltage controller.

[0013]FIG. 6 shows a transmission protocol, and

[0014]FIG. 7 shows bit decoding.

[0015]FIG. 8 shows a proposal for a method or the functional scope for a voltage controller with an interface, and

[0016]FIG. 9 shows an exemplary embodiment of a voltage controller with an interface in the form of a basic circuit diagram.

[0017] In Tables 1-5, various items of information for the interface between the voltage controller and the on-board electrical system are shown; Table 2 shows possible commands, Table 3 possible items of information, Table 4 a start/stop sequence, and Table 5 an error evaluation.

DESCRIPTION

[0018] In FIG. 1, a first data station 31 and a second data stations 32 are shown, which communicate with one another by a transmission line 15. The first data station 31 has a microprocessor 33 and an interface 2, which communicate with one another over a plurality of lines 34. The second data station 32 has a logic circuit 35, which communicates with an interface 3 over a plurality of lines 36. The interfaces 2 and 3 have the task of preparing data, which they receive from the microprocessor 33 or the logic unit 35, for transmission over the transmission line 15, or correspondingly processing data, which the interfaces 2, 3 receive from the transmission line 15, for the microprocessor 35 or the logic unit 35. What is essential here is that the interfaces 2, 3 are embodied such that three different states are realized on the transmission line 15.

[0019] The different states that are realized on the transmission line 15 are shown in a graph in FIG. 2. The time t is plotted over the signal s; the signal here is realized in the form of different voltage levels V0, V1 and V2. V2 is the highest voltage level, and V0 is the lowest voltage level. In the time period or length of time t1, the transmission line 15 is in the state repose, which is realized here by the voltage level v2. For the ensuing description it will be assumed that the first data station 31 is transmitting a signal to the second data station 32. In the time period t2, the interface 2 pulls the transmission line 15 to the voltage level V1. This indicates that a data transmission is about to be done. An advance warning to the second data station 32 of this kind can be utilized for instance to activate an appropriate program in the second data station 32 that performs the processing of the data, as long as the second data station 32 likewise has a microcomputer for evaluating the data. The time period t2 and the subsequent time period t3, in which the repose level V2 is reestablished on the transmission line 15, are dimensioned in terms of their length such that sufficient time is available for preparing the second data station 32 for the reception of data. The bus level V2 subsequently represents the bit state “high”, while the bus level V1 represents the bit state “zero”. The transmission line 15 can also be applied to the level V0 by the interfaces 2, 3, as is the case for the time period t4. This time period t4 having the voltage level V0 represents a synchronization signal on the transmission line 15. This synchronization signal is generated for instance by the microprocessor 33 and then sent on to the interface 2 over one of the lines 34. The synchronization signal is also known as a clock signal or clock (CLK). As a function of this synchronization signal of the microprocessor 33, the interface 2 generates the synchronization signal on the transmission line 15, by pulling the transmission line 15 to the voltage level V0 for a predetermined minimum time period t4. The minimum time period is designed such that the receiving second data station 32 can reliably detect this signal on the transmission line 15. The receiving second data station 32 then uses this synchronization signal to generate an internal synchronization signal, with which the processing of the data is clocked. The receiving data station can be synchronized to the end of the time period t4, for example. As can be seen from FIG. 2, each time after the bus level V0 has been assumed either the bus level V1 or the bus level V2 is assumed; that is, after each synchronization signal, either a high bit or a low bit is transmitted. The receiving data station must therefore, each time after the end of the voltage state V0, sample the voltage level on the transmission line 1, in order to detect a high bit or a low bit. In the period t5, for instance, a high bit is transmitted with the voltage level V2. In the time period t6, a synchronization signal is again present, and in the time period t7, a high bit is again indicated by the voltage level V2. After the synchronization signal in the time period t8, a low bit is indicated on the transmission line 15 in the time period t9. In the time period t10 a synchronizing bit and in time period t11 a subsequent low bit are again transmitted. Up to this time, in FIG. 2, the synchronization signals have each been represented by time periods t4, t6, t8, t10 of equal length, and the bit states have been represented likewise by time periods t5, t7, t9 and t11 of equal length. Because of the simple synchronization, however, it is unnecessary for the time period for the synchronization signal or the individual data bit to have a predetermined length, as long as a certain minimum length, which is required for adequate identification of the voltage level on the transmission line, is adhered to. In the time period t12 and the time period t13, by way of example, a synchronization signal and a low bit respectively, are shown, which have time periods t12 and t13 that differ from one another. Thus the transmission method presented here is not required to adhere to predetermined lengths for the signal levels.

[0020] In FIG. 1, only a single data line 15 has been shown, which by way of example can be embodied by a wire that connects the two data stations 31 and 32 to one another. Alternatively, it is also possible instead of the single data line 15 to have two data lines, which are operated with a differential signal. In that case, the signal in FIG. 2 would not comprise an absolute voltage level on a transmission line but rather the difference between the voltage levels that are present on the two data lines. Instead of voltage levels, one or two data lines over which currents flow may also be used. Optical fibers are also suitable as a transmission line; in that case, the signal could comprise different intensities of light.

[0021] It has been stated with regard to the first data station 31 that it has a microprocessor 33, while the second data station 32 has a logic circuit. The method of the invention is especially advantageous for transmitting data if one of the data stations involved has high “intelligence”, and the other data station or stations are embodied comparatively simply. The smart data station 31 therefore has a microcomputer 33, which can process many complex tasks. The microcomputer 33 also has an internal clock, with which an internal clock signal is available for generating synchronization signals. This synchronization signal is then transmitted by the transmission line 15 and serves as a standard for the processing of the data in the second data station 32, which is embodied simply. The second data station 32 for instance has only a simple logic circuit 35, which is clocked by the synchronization signal. A simple example of such a logic circuit is described in conjunction with FIG. 4. It is also possible to embody the data station 31 as a logic circuit, which has a source for a synchronization signal. This station can then transmit items of information to the data station 34 at spaced-apart times, for instance. Moreover, the data station may have a microcomputer that outputs data to be transmitted over parallel bus lines to a logic unit that then performs the actual transmission over the data line 15.

[0022] In FIG. 1, the data exchange between a first and a second data station 31, 32 is described. However, the method of the invention can equally well be employed if more data stations are involved, and in that case at least one of the data stations is capable of generating a synchronization signal. The data to be transmitted should in that case have addresses, which clearly show the intended destination station at the time of the particular data.

[0023]FIG. 3 shows a concrete embodiment of the interfaces 2 and 3. In the interface 2, the transmission line 15 is connected to a node 4 of a voltage divider comprising the resistors 5 and 6. The node 4 is connected to a supply voltage VCC via the resistor 5 and a switch 15. The node 4 is also connected via the resistor 6 to the collector of a transistor 7, whose emitter is connected to ground. The base of the transistor 7 is connected to a line Out-Data to the microprocessor 33, not shown here. Also in the interface 2, the transmission line 15 is connected to the collector of a transistor 8, whose emitter is connected to ground. The base terminal of the transistor 8 is connected to a line Out-CLK to the microprocessor 33, not shown. The transmission line 15 in the interface 2 is also connected to one input of a comparator 9, and the comparator has a further input for a comparison voltage V. The comparator 9 has an output In-Data, which is connected to the microprocessor 33.

[0024] In the interface 3, the transmission line 15 is connected to input each of a comparator 10 and a comparator 11. Each of these comparators 10, 11 also has a further input for a comparison voltage V. The comparator 10 has an output In-Data, which is connected to the logic circuit 35, not shown. The comparator 11 has an output IN-CLK, which is likewise connected to the logic circuit. Also in the interface 3, the transmission line 15 is connected via a resistor 12 to the collector of a transistor 13. The emitter of the transistor 13 is connected to ground. The base of the transistor 13 is connected to the logic circuit 35 via a line Out-Data.

[0025] If the switch 15 of the interface 2 is closed, then the transmission line 15 is connected to the potential VCC via the resistor 5, which establishes the repose potential of V2 on the transmission line 15. If a signal is present on the line Out-Data the transistor 7 is switched to be conducting, and the transmission line is pulled to a potential V1 by the voltage divider comprising the resistors 5 and 6. If a signal is present on the line Out-CLK, then the resistor 8 is made conducting, and the transmission line 15 is connected at low impedance to ground, so that a potential V0 is then established on the transmission line. The interface 2 thus has all the means for realizing all three voltage levels V2, V1 and V0, as a function of control signals of the microprocessor 33, on the transmission line 15.

[0026] In the interface 3, the comparison voltage V is selected for the comparator 10 in such a way that a signal, such as a high level is present at the output In-Data of the comparator if the transmission line 15 is at the value V2. The comparison voltage V is also selected such that at the output In-Data no signal or a low signal is present if the transmission line 15 is at the voltage level V1. Typically, a comparison voltage that is between V1 and V2 will be chosen for this purpose. The comparator 11 has a comparison voltage V which is selected such that the third state, that is, the voltage level V0, can be reliably detected. To that end, the comparison voltage is between V0 and V1. The interface 3 thus has means for distinguishing the first, second and third voltage levels on the transmission line 15, and as a consequence of making signals available for the logic circuit 31. On the basis of the synchronization signals that are generated by the interface 2 on the transmission line 15, a clock signal is made available in the interface 3 on the line In-CLK (CLK=clock), by which signal the logic circuit 35 is supplied with a clock signal. The control of the interface 2 by the microprocessor 33 is done such that before each high bit or low bit is output, a synchronization signal is output. This synchronization signal represents the synchronization signal for the second interface and the logic unit 33 connected to it, with which synchronization signal the processing of the bit levels in the interface 2 and the logic unit 35 is clocked. Means are also indicated in FIG. 3 that allow data to be transmitted back from the interface 3 to the interface 2. To that end, the interface 3 has the transistor 13, which is connected to the line Out-Data of the logic circuit 35. Via the resistor 12, which together with the resistor 5 of the interface 2 forms a voltage divider, the transmission line 15 can thus be subjected selectively to the potential V2 or V1. The comparator 9 of the interface 2 is connected to a corresponding comparison potential V, which then allows a distinction to be made between the voltage states V2 and V1 on the transmission line 15. However, care must be taken that the interface 3 not have any means which make it possible to realize the third state with the voltage level V0 on the transmission line 15. Only the interface 2 has the means to do that. This if a data transmission from the interface 3 to the interface 2 is planned, then the clock signal continues to be furnished only by the interface 2. To that end, the interface 2 furnishes a synchronization signal on the transmission line 15 by connecting the transmission line to ground via the transistor 8. If the transistor 8 then blocks, then as a function of the switching state of the transistor 13 of the interface 3, a corresponding voltage level, V2 or V1, will be established on the transmission line 15.

[0027] The switch 15 can also be utilized to put the data station 32, from a standby state in which it has low current consumption, into an operating state. To do so, the transmission line or data line 15 would then also have to be connected to a component which in the standby state detects the imposition of the voltage level V2 on the data line 15. In the case of a controller for a generator, the switch 16 would be coupled with the ignition key.

[0028] If a plurality of interfaces are connected to the transmission line 15, then the entire system is designed such that at any particular time, only a single station can generate a synchronization signal on the transmission line 15. A particular advantage of this system is that only the station that generates the synchronization signal needs to have a certain intelligence and must possess the means for generating a synchronization signal. The other stations can be embodied especially simply; in particular, no oscillating circuits with which a clock signal is generated need be present in these stations. Moreover, these stations may be embodied as a simple logic circuit.

[0029] In FIG. 4, a simple example for a logic circuit 35 is shown. This example relates to a controller for a generator of the kind used in a motor vehicle. In such a generator, it is desirable for an engine control unit to be capable of transmitting a signal to a generator controller, with which signal the closed-loop control voltage of the generator controller is established. The object is thus by means of a transmission line to transmit an analog signal, which corresponds to a voltage, to the controller. Since numerous stray voltages occur in a motor vehicle, it is not possible to transmit such an analog signal directly, since the voltage levels on the line can vary as a consequence of interference. However, the controller need merely understand the voltage signal, transmitted in the form of bits, and otherwise can be designed comparatively simply. A controller of this kind, which is located downstream of an interface 3, is shown in FIG. 4. The controller has a shift register 41, whose data input is connected to the line In-Data of the interface 3. The shift register 41 also has a clock input 46, which is connected to a delay element 45. A delay elements of this kind can be any arbitrary component with which a brief delay in the signal is associated. This is necessary, since after the transition from V0 to one of the bit levels V1 or V2, a defined signal level must first be established at the data input of the shift register 41. If the sequence of voltage levels as shown in FIG. 2 has been sent over the transmission line 15, then the value 11000 is written into the shift register 41. This value is then present at the parallel output lines 42 of the shift register 41 and serves as an input value for a digital/analog converter 43. Depending on the bits present on the parallel lines 42, an output value, for instance an analog output voltage, is then output over the output line 44 of the digital/analog converter. Such a voltage value then represents the switching level of the generator controller.

[0030] The shift register 41 also has a reset input 48, with which the contents of the shift register 41 can be set to a predetermined starting value. The reset input 48 is connected to a reset component 47, which is connected to the In-Data line and the In-CLK line. The reset component 47 detects whether a voltage change has occurred on the line In-Data without a signal having previously been applied to the In-CLK line. If so, then a reset signal is generated, with which the shift register 41 is set to the starting value. Such a signal is used in FIG. 2, in the period t2, to signal the beginning of a data transmission. Thus the shift register 41 can always be reloaded on the basis of a predetermined starting value.

[0031] As can be seen in FIG. 4, on the reception side simple logical circuits can be utilized for evaluating the data words that are transmitted digitally over the transmission line 15. A certain intelligence for operating the data transmission need essentially be present only in the station that also makes the synchronization signal available. The system is thus especially highly suitable if a smart main station responds to one or more comparatively simply designed stations.

[0032] Further features of the invention are shown in FIGS. 5-9. With a bit-synchronized interface, a method for data transmission can be realized in which the information to be transmitted can be represented by two different voltage levels.

[0033] A bit-synchronized interface can for instance be used in a motor vehicle, where it is especially suitable for the connection between the voltage controller and the on-board electrical system, or between the voltage controller and the engine control unit having the digital engine electronics.

[0034]FIG. 5 shows the layout of the interface. If this interface is used with an on-board vehicle electrical system, already known in principle, that has a voltage controller as shown in FIG. 9, then a voltage control system can be put together that assures an optimal battery charging state and that improves the charge balance over conventional systems. In the case of a multifunction controller, optimal connections with the engine control unit of the engine electronics are possible without involving additional costs. Fast and reliable control can be accomplished on site with central generation of controlling variables.

[0035] The individual possibilities are attained by the characteristics shown in Tables 1-5. They will be understood in conjunction with the drawing figures and the details described hereinafter. TABLE 1 Interface Between Controller and On-Board Electrical System Transmission rate of the interface? Precise command definition for the controller? Address allocation and hence prioritization of the controller? Maximum number of receivers for this interface? -- > Number of bits necessary for addressing

[0036] TABLE 2 Interface Between Controller and On-Board Electrical System Possible Commands Write: Control voltage offset 6 bits (increments of approximately 100 mV) Control: ON/OFF control LRD 3 bits: 0, 2, 4, . . . , 14 s Measurement mode

[0037] TABLE 3 Interface Between Controller and On-Board Electrical System Possible information Read: DFM value 5 bits (resolution approximately 3%) Error/status flag 6 bits: Overvoltage Undervoltage Field end stage short circuit toward plus Field interruption/short circuit to ground Belt breakage Full-load monitor

[0038] TABLE 4 Interface Between Controller and On-Board Electrical System Start/stop sequence 1. Detect IGNITION SWITCH ON via HIGH level at interface; controller is activated, but no excitation 2. Cyclical deactivation (maximum 2-second intervals) of control by transmitting the control-OFF command 3. If control-OFF is not set within 2 s, the controller enters the normal control mode --> emergency startup via terminal V 4. If detection of generator turning without IGNITION SWITCH ON, the controller enters the normal control mode --> emergency startup via terminal V 5. If IGNITION SWITCH OFF and generator is stopped, the controller is turned off

[0039] TABLE 5 Interface Between Controller and On-Board Electrical System Error evaluation 1. If no valid message is transmitted within 2 s, then the controller with all its parameters enters the default state 2. Errors are transmitted to the engine control unit and processed and optionally indicated by it 3. An unsuccessful connection to the controller evaluates the engine control unit

[0040] In FIG. 5, the interface between a voltage controller 50 and the digital engine electronics 51, for instance the control unit of an internal combustion engine or a so-called on-board electrical system control unit or other electronics, is described. The connection is made solely via a line 52, which is located between the amplifier 53 of the controller and the amplifier 54 of the digital engine electronics. The signal DataIN occurs at the output of the two amplifiers 53, 54. The base of a transistor 55 of the controller 50, whose collector is connected to the line 52 and whose emitter is connected to ground, is supplied with the signal DataOUT. In the digital engine electronics DME 51, there is a transistor 56, whose emitter is connected to ground and whose collector is connected to the line 52. Via a resistor 57 and a switching means 58, the collector of the transistor 56 can be applied to battery voltage UB. The base of the transistor 56 is supplied with the signal DataOUT.

[0041] With the interface shown in FIG. 5 between the controller 50 and the DME 51, a method according to the invention for transmitting data and for receiving data can be realized. A bidirectional, bit-synchronized transmission of items of bit information can be carried out with the information bits SYNC, 0 and 1. The three items of information are distinguished from one another by a pulse-interval-encoded single period. The signal course is shown in FIG. 7. If such an item of information is sent over the line 52, then the desired data can be transmitted. For synchronization, continuous items of SYNC information are sent by the master, and only during a transmission message of n bits are either 0 or 1 items of information transmitted from or to the master. That is, a sequence of Sync-pulses-transmission message-Sync-pulses is transmitted. FIG. 6 shows a transmission protocol that indicates the course over time of the signal transmitted. DIR indicates the bit for the data direction; transmission is either from the master (DME) 51 to the slave (controller) 50, or from the slave (controller) to the master (DME). ADDRESS indicates bits for which the following applied: if transmission is from the master (DME), this indicates the address of the receiver; if transmission is from the slave (controller), this signal portion indicates the address of the slave.

[0042] COMMAND indicates commands or a register index. DATA indicates the transmission or reception data. P stands for parity of the sender and ACKN indicates the acknowledgement by the receiver.

[0043] Since in the bidirectional bit-synchronized transmissions of items of bit information, shown in FIGS. 6 and 7, work is done with only two voltage levels, and the various items of information are bound into different pulse-interval ratios, the full voltage rise can be utilized and thus a maximum signal to noise ratio can be achieved. The signal SYNC always comes from the master; it is therefore possible to use one-chip oscillators without quartz, since the possibility of synchronization exists. The synchronization can be done to the bit information; that is, errors and tolerances apply only to individual bits and are not added together in the transmitted word. The bidirectional transmission is done, as already noted, simply by lengthening the SYNC signal a single time to yield a 0 datum or a 1 datum. Prioritizing is possible, for instance because the 1 datum is longer than the 0 datum.

[0044]FIG. 8 provides a summary of the basic functions as well as possible convenience functions, listing first a two-level signal. Also listed are a pulse width modulated signal, a bit-synchronized interface, and a CAN bus. The bit-synchronized interface and the CAN bus can be expanded for the basic functions and the convenience functions. As the basic function, a characteristic curve for the control function is shown. Convenience functions are a load-response function, a DF monitor, with which the signal applied to the terminal DF is processed. Another convenience function is an error indication, with which the actual indication as well as diagnosis can be accomplished. Other functions are possible.

[0045]FIG. 9 shows one possible use of the interface of the invention or the method of the invention for an on-board vehicle electrical system. This on-board vehicle electrical system in a known manner includes a rotary current generator 90, the brush holder 91 with the terminals B+, DF and V. The controller 92, which is equivalent to the controller 50 in FIG. 5, has the D-terminal and in a known manner includes a power portion 93 and a control portion 94. The control portion 94 of the controller 92 is connected to the DME 95, which by way of example is equivalent to the digital engine electronics 51 of FIG. 1, via the interface COM. Between the DME 95 and the controller 92, control signals ST and diagnosis signals D1 are exchanged. A connection, not shown in further detail, of the charge indicator light 96 makes an error indication possible. Of the on-board electrical system 97, only the battery 98, a consumer 99, and the starter 100 are shown. The consumer 99 can be connected to the positive pole of the battery 98 via switching means 100, and the starter 100 can be connected to the terminal Kl.15 via the switch 102 (ignition switch ZS), which in turn leads via the starter to terminal Kl.30 and thus to the battery 98.

[0046] The generator current IG is tapped via the terminal B+ and leads to the positive terminal of the battery 98. Also connected to the output of the rectifier bridge 104, which is formed for instance by six Zener diodes, is a capacitor 105. Otherwise, of the rotary current generator 90, only the field winding 106 and the stator windings 107, 108 and 109 are shown.

[0047] The data transmission can proceed between the control unit DME 95 and the voltage controller 92, or its control portion 94; a data transfer in both directions is possible. Items of information can thus be delivered by the voltage controller to the control unit 95; the control unit 95 can in turn perform the desired control functions, such as the basic and convenience functions listed in FIG. 8. 

1. A method for transmitting data via a transmission line (15) by transmitting a sequence of a first or a second state, which can be distinguished from one another, over the transmission line, Which states represent a high bit or a low bit, characterized in that a third state, which can be distinguished from the first two states, can be generated on the transmission line (15), and that the third state is used as a synchronization signal.
 2. A method for transmitting data from a first device, which is connected to a second device by at least one transmission line, wherein sequences of a first or second state, which can be distinguished from one another, are generated on the transmission line, characterized in that by means of the two states, one synchronization pulse and two information pulses are formed, and the durations of the pulses differ from one another.
 3. The method of claim 1 , characterized in that the synchronization signal is formed by putting the transmission line into the third state for a predetermined minimum time.
 4. The method of claim 3 , characterized in that for a predetermined minimum time, the data line is put into the first or second state in order to indicate a high bit or low bit, and that before each high bit or low bit, a synchronization signal is transmitted.
 5. The method of one of the foregoing claims, characterized in that the transmission line has a state of repose, in which it is kept in one of the three states, and that the beginning of a data transmission is indicated by the fact that the transmission line is put into some state other than the state of repose.
 6. The method of one of the foregoing claims, characterized in that the three different states are realized by generating different voltage levels on an electrical conductor.
 7. The method of claim 2 , characterized in that the first device is a microprocessor, in particular a control unit, in a motor vehicle, and the second device is the voltage controller of the motor vehicle.
 8. The method of claim 2 or 7 , characterized in that a plurality of receivers are present, and a transmission protocol is generated.
 9. An interface for outputting data, which is connected to a transmission line, and the interface has first means for generating a sequence of a first or a second state, distinguishable from one another, on the transmission line, which states represent high bits or low bits, characterized in that second means are provided, so as by conversion of a synchronization signal on the data line to generate a third state, which can be distinguished from the first and second states.
 10. The interface of claim 9 , characterized in that the three different states are realized by means of voltage levels on an electrical conductor.
 11. The interface of claim 10 , characterized in that the first means have a voltage divider with a first resistor (5) and a second resistor (6); that the first resistor (5) is disposed between a first voltage (VCC) and a node; that the second resistor is disposed between the node and a switch; and that the switch is disposed between the second resistor (6) and a second voltage (ground); that the switch is switchable selectively for outputting a high bit or a low bit; and that the transmission line (15) is connected to the node (4).
 12. The interface of claim 11 , characterized in that the second means have a switch, with which the transmission line can be connected to the first or the second voltage; and that the switch can be switched as a function of synchronization signals.
 13. The interface of claims 10-12, characterized in that a data line (Out-Data) and a synchronization line (Out-CLK) for triggering the switches are provided; and that the data line (Out-Data) and the synchronization line (Out-CLK) are connected to a microprocessor, in particular a microprocessor of an engine control unit.
 14. An interface for receiving data, which is connected to a transmission line, the interface having third means for detecting a sequence of a first or second state, distinguishable from one another, on the transmission line (15), which states represent a high bit or a low bit, characterized in that fourth means are provided for detecting a third state on the transmission line (15), which state is distinguishable from the first and second states, and therefrom to generate a synchronization signal.
 15. The interface of claim 14 , characterized in that the three states are realized by voltage levels that are distinguishable from one another.
 16. The interface of claim 14 , characterized in that the third means and the fourth means each have one comparator; that one terminal of each of the comparators is connected to the transmission line, and one second terminal of each of the comparators is connected to a comparison voltage.
 17. The interface of claims 14-16, characterized in that the comparators are connected to a data line (In-Data) and a synchronization line (In-CLK), with which data and a synchronization signal can be transmitted to a receiver, in particular a controller for a generator.
 18. The interface of claims 14-17, characterized in that fifth means (12, 13) are provided for generating the first or the second state on the transmission line (15) in order to output a high bit or a low bit; and that these means are actuated only as a consequence of a received synchronization signal.
 19. An interface for outputting data, which has means for generating sequences of a first or a second state, distinguishable from one another, on a transmission line, characterized in that the states are formed such that one synchronization pulse and two information pulses are created, the durations of the pulses differing from one another. 